import java.util.Scanner;

public class 求平均数 {

    public static void main(String[] args) {
        Scanner scan = new Scanner(System.in);
        int num;
        int sum = 0, count = 0;
        while (true) {
            num = scan.nextInt();
            if (num < 0)break;
            count++;
            sum += num;
        }//判断如果数是小于零则进入平均数计算
        scan.close();
        if (count > 0) {
            double avg = (double)sum / count;
            //输出格式为：System.out.println(String.format("%.2f",avg));
            System.out.println(String.format("%.2f", avg));
        }


    }
}